- Receipt of concomitant chemo-radiotherapy. The chemotherapy-part must have been platinum-based, must have been administered with a minimum of two cycles overlap with radiotherapy (one cycle lasts either 3 or 4 weeks depending on the chemotherapy regimen), and a minimum of two platinum-based chemotherapy administrations must have been given during radiotherapy. Purely radio sensitizing doses of chemotherapy are not acceptable. Radiotherapy must have delivered a radiation dose of >= (greater than or equal to) 50 Gray (Gy). Induction or consolidation chemotherapy is allowed and if given, should be accounted as part of primary thoracic chemoradiotherapy. Subjects must have completed the primary thoracic chemo-radiotherapy at least four weeks (28 days) and no later than 12 weeks (84 days) prior to randomization. Subjects who received prophylactic brain irradiation as part of primary chemo-radiotherapy are eligible